'use strict';

function preserveCamelCase(str) {
  let isLastCharLower = false;
  let isLastCharUpper = false;
  let isLastLastCharUpper = false;

  for (let i = 0; i < str.length; i++) {
    const c = str[i];

    if (isLastCharLower && /[a-zA-Z]/.test(c) && c.toUpperCase() === c) {
      str = str.substr(0, i) + '-' + str.substr(i);
      isLastCharLower = false;
      isLastLastCharUpper = isLastCharUpper;
      isLastCharUpper = true;
      i++;
    } else if (isLastCharUpper && isLastLastCharUpper && /[a-zA-Z]/.test(c) && c.toLowerCase() === c) {
      str = str.substr(0, i - 1) + '-' + str.substr(i - 1);
      isLastLastCharUpper = isLastCharUpper;
      isLastCharUpper = false;
      isLastCharLower = true;
    } else {
      isLastCharLower = c.toLowerCase() === c;
      isLastLastCharUpper = isLastCharUpper;
      isLastCharUpper = c.toUpperCase() === c;
    }
  }

  return str;
}

module.exports = function (str) {
  if (arguments.length > 1) {
    str = Array.from(arguments)
      .map(x => x.trim())
      .filter(x => x.length)
      .join('-');
  } else {
    str = str.trim();
  }

  if (str.length === 0) {
    return '';
  }

  if (str.length === 1) {
    return str.toLowerCase();
  }

  if (/^[a-z0-9]+$/.test(str)) {
    return str;
  }

  const hasUpperCase = str !== str.toLowerCase();

  if (hasUpperCase) {
    str = preserveCamelCase(str);
  }

  return str
    .replace(/^[_.\- ]+/, '')
    .toLowerCase()
    .replace(/[_.\- ]+(\w|$)/g, (m, p1) => p1.toUpperCase());
};
